As breeding season for Western toads winds down, a little-noticed migration is taking place at four ponds and lakes in Pierce County as the fingernail-sized amphibians hop toward surrounding forests.

This year’s migration has been more drawn out than usual, although wildlife experts are not sure why.

“We’ve seen this kind of slow, steady migration this year and that’s not usual for them,” said Jessica Moore, conservation program coordinator at Northwest Trek Wildlife Park.

The Eatonville park hosts two of the known breeding areas for the Western toads, whose numbers have been dwindling in Pierce County for decades.

The state Department of Fish and Wildlife considers them a “species of concern” because their numbers are dropping in South Puget Sound and the lower Columbia Gorge. Experts say there’s no cause for concern yet, and they’ll continue to monitor the toads in hopes of learning more about the elusive species.

Western toads, like other amphibians, are considered an indicator species, which means their health reflects that of their environment.

Field biologists don’t have a strict regimen for checking on the toads. At Northwest Trek, Moore and her co-workers try to visit the ponds weekly to document what they see and compare it with previous years.

Anywhere from a dozen to four dozen toads return each year to breed in two wetland ponds on a 100-acre plot the wildlife park.

They usually arrive in late March or early April once overnight water temperatures top 42 degrees. Breeding can last two weeks, with one female laying thousands of eggs.

The eggs are long strings with a diameter thinner than a pencil. They resemble black pearls.

“Western toads lay eggs unlike any other amphibian in the Northwest,” Moore said.

The tadpoles eventually metamorphose into toadlets, which hover on the edges of the water before finding their way to land for the rest of the year. The toads seek out the water only for breeding.

That’s why Northwest Trek workers strive to maintain the ponds exactly as they are, taking great pains ensure no trees shade the water and the water depth stays shallow.

With the toads’ migration route being on land not accessible to the public, it makes the job a little easier.

“We’re managing to maintain Toad Pond exactly the way it is right now because that’s the way they like it,” Moore said.